Report of the International Committee on Atomic Weights

Clark, F. W.; Ostwald, W.; Thorpe, T. E.; Urbain, G.

doi:10.1039/ca908940x001

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(2 citation statements)

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“…DISCUSSION Cellular studies of intact Aplysia mechanosensory neurons (9,11,13,33,34) suggested that the Ca2+/CaM-sensitive adenylyl cyclase may be an important site of stimulus convergence, contributing to activity-dependent enhancement of presynaptic facilitation in these neurons and to associative modification of the withdrawal reflex. In both conditioning of this reflex and in activity-dependent facilitation, the associative change depends upon the sequence of pairing (21,22); therefore, it seemed possible that activation of cyclase by Ca2+ and transmitter would depend upon the order of their arrival. In the present study, we found that when brief exposures to Ca2+ and 5-HT were paired, they interacted in stimulating the cyclase in a temporally asymmetric manner.…”

Section: Resultsmentioning

confidence: 99%

“…There is also a sequence requirement: associative learning does not result from backward pairing in which the US begins first during training, even when the two stimuli overlap temporally (21). Activity-dependent presynaptic facilitation has similar sequence requirements for pairing: sensory neuron activity is most effective in enhancing the response to facilitatory transmitter if it precedes the transmitter (22).…”

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confidence: 99%

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Temporal asymmetry in activation of Aplysia adenylyl cyclase by calcium and transmitter may explain temporal requirements of conditioning.

Yovell

Abrams

1992

Proc. Natl. Acad. Sci. U.S.A.

122

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Cellular experiments have suggested that during dassical conditioning of the gill and siphon withdrawal reflex ofAplysia, adenylyl cyclase may serve as a molecular site of convergence for Ca2+ and serotonin (5-hydroxytryptamine; 5-HT), the cellular representations of the conditioned and unconditioned stimuli (CS and US). We explored the possible molecular basis of the behavioral requirement that the CS and US be paired within a narrow time window and in the appropriate order. To examine the temporal interactions of brief pulses of Ca2+ and 5-HT in stimulating Aplysia neural cyclase, we used a perfused-membrane cyclase assay. When briefpulses of Ca2W and 5-HT were paired, cyclase activation depended upon the sequence of the pulses: peak cyclase activation was greater when the Ca2+ pulse iediately preceded the 5-HT pulse. Eamination of the rising phase of 5-HT stimulation suggested that a Ca+ prepulse might accelerate the onset of activation by 5-HT, without affecting the final level of activation achieved with prolonged 5-HT exposure. The observed interactions between Ca2+ and transmitter in activating cyclase could contribute importantly to the temporal requirements of conditioning for CS-US pairing.

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